1988 JEEP CHEROKEE engine

IDLE SPEED ACTUATOR (ISA) MOTOR
1) Adjust ISA motor plunger to establish initial position of
plunger only if motor has been removed or replaced. Remove air filter
elbow and start engine. Run engine until engine reaches normal
operating temperature. Turn A/C off (if equipped).
2) Connect tachometer leads to diagnostic connector D1,
attaching negative lead to terminal D1-3 and positive lead to
terminal D1-1. See Fig. 4. Turn ignition off. ISA motor plunger
should move to fully extended position.
3) When ISA motor plunger is fully extended, disconnect ISA
motor wiring connector and start engine. Engine speed should be
3300-3700 RPM. If incorrect, turn hex head screw at end of plunger to
provide engine speed of 3500 RPM.
4) Fully retract ISA motor by holding closed throttle (idle)\
switch plunger inward as throttle is opened. Closed throttle switch
plunger should not touch throttle lever in closed position. If
contact is made, check linkage and/or cable for binding or damage.
Repair as necessary.
5) Connect ISA motor wiring harness connector and turn
ignition off for 10 seconds. ISA motor should move to fully extended
position. Start engine. Engine speed should be 3500 RPM for short
period of time and then decrease to normal idle speed.
6) Turn ignition off. Disconnect tachometer. After final
adjustment of ISA motor, use thread penetrating sealant (Loctite 290)
on adjustment screw to prevent movement and maintain adjustment.
NOTE: If adjustment screw must be moved after thread sealant
hardens, loosen threads by heating screw with flameless heat
such as soldering gun. DO NOT use flame or torch type of
heat as damage to ISA motor will result.
FUEL PRESSURE REGULATOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.
1) Replacement fuel pressure regulator must be adjusted to
establish correct pressure. Remove air filter elbow and hose. Connect
tachometer leads to diagnostic connector D1, attaching negative lead
to terminal D1-3 and positive lead to terminal D1-1. See Fig. 4.
Remove screw plug and install fuel pressure test fitting.
NOTE: Fuel pressure test fitting is not included with throttle
body. Fitting (8983 501 572) must be obtained separately.
2) Connect fuel pressure gauge to test fitting. Start engine
and increase speed to approximately 2000 RPM. Turn Torx head screw at
bottom of regulator to set correct pressure. Turning screw inward
increases pressure and turning screw outward decreases pressure. See
Fig. 3 .
3) All models require fuel pressure of 14.5 psi (1.0 kg/cm
).
Install lead sealing ball to cover regulator adjustment
screw after adjusting fuel pressure. Turn ignition off. Remove
measuring equipment and test fitting. Install original plug screw and
air filter assembly.

3) Return throttle plate to closed throttle position (M/T),
or maintain throttle plate in closed position (A/T). Check sensor
output voltage. To do so, disconnect voltmeter positive lead from
terminal "C" and connect it to terminal "A" (top) of sensor (M/T), o\
r
from terminal "A" and connect it to terminal "B" (A/T).
4) Move and hold throttle plate in wide open throttle
position (M/T), or maintain throttle plate in closed position (A/T).\
Ensure throttle linkage contacts stop. Note voltmeter reading. Output
voltage should be 4.6-4.7 volts (M/T), or .2 volt (A/T).
5) If output voltage is incorrect, loosen bottom sensor
retaining screw and pivot sensor in adjustment slot for a coarse
adjustment. Loosen top sensor retaining screw for fine adjustments.
Tighten screws after adjustment.
TESTING & TROUBLE SHOOTING
PRELIMINARY CHECKS & PRECAUTIONS
Subsystem Checks
Before testing fuel injection system for cause of
malfunction, check that following subsystems and components are in
good operating condition:
* Battery and charging system.
* Engine state of tune.
* Emission control devices.
* Fuel system pressure and delivery volume.
* Wiring connectors at components.
General Precautions
In order to prevent injury to operator or damage to system
or component parts, use following techniques:
* Turn ignition off before connecting or disconnecting any
component parts.
* DO NOT apply DC voltage greater than 12 volts or any AC voltage
to system.
* Disconnect battery cables before charging.
* Remove ECU from vehicle if ambient temperature could exceed
176

F (80
C).
* DO NOT modify or circumvent any system functions.
RESISTANCE & VOLTAGE TESTS
MAT Sensor
1) Disconnect wiring from MAT sensor. Using high input
impedance digital volt-ohmmeter (DVOM), check resistance of sensor.
Resistance should be less than 1000 ohms when engine is warm. Replace
sensor if it does not fall within range shown in
TEMPERATURE-TO-RESISTANCE VALUES table.
2) Test resistance in wiring harness between ECU connector
terminal No. 32 and sensor connector terminal. Also test resistance
in wiring harness between ECU harness terminal No. 14 and sensor
connector terminal. See Fig. 5. Repair wiring harness if open circuit
or resistance greater than one ohm is indicated.
Coolant Temperature Sensor (CTS)
1) Disconnect wiring harness from CTS. Using high input
impedance digital volt-ohmmeter (DVOM), check resistance of sensor.
Resistance should be less than 1000 ohms when engine is warm. Replace
sensor if it does not fall within range shown in
TEMPERATURE-to-RESISTANCE VALUES table.

2) Test resistance in wiring harness between ECU harn
terminal No. 32 and sensor connector terminal. Also test resistance
in wiring harness between ECU harness terminal No. 15 and sensor
connector terminal. See Fig. 5. Repair wiring harness if open circuit
or resistance greater than one ohm is indicated.
TEMPERATURE-TO-RESISTANCE VALUES (CTS & MAT SENSOR) TABLE
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F
C Ohms
(Approximate)
212 ......................... 100 ........................... 185
160 ......................... 70 ............................ 450
100 ......................... 38 ........................... 1600
70 .......................... 20 ........................... 3400
40 ........................... 4 ........................... 7500
20 .......................... -7 ......................... 13,500
0 ........................... -18 ........................ 25,000
-40 ......................... -40 ....................... 100,700
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Throttle Position Sensor (TPS) Test
Turn ignition on. Check voltage at terminal connector
without disconnecting from TPS. Terminal "A" (M/T), or terminal "B"
(A/T ) is output voltage, which should be 4.6-4.7 volts at wide open
throttle (M/T), or .2 volt at closed throttle (A/T). Terminal "B"
(M/T), or terminal "A" (A/T) is sensor ground. Terminal "C" (M/T),\
or
terminal "D" (A/T) is input voltage, which is about 5 volts.
Closed Throttle (Idle) Switch Test
NOTE: ALL testing of idle switch must be done with ISA motor
plunger in fully extended position. If switch cannot be
tested without extending plunger, it is possible that ISA
motor has failed. See IDLE SPEED ACTUATOR MOTOR ADJUSTMENT.
1) Turn ignition on. Check idle switch voltage at diagnostic
connector D2, between terminals No. 13 and 7. See Fig. 4. At closed
throttle, voltage should be near zero volts. When switch is off
closed throttle position, voltage reading should be greater than 2
volts.
2) If voltage is always zero, test for short to ground in
harness or switch. Also check for open circuit between switch and
terminal No. 25 of ECU connector. If reading is always greater than 2
volts, check for open circuit in wiring harness between switch
connector and ECU. Also check for open between ground and switch
connector. Replace or repair wiring harness as necessary.
Manifold Absolute Pressure (MAP) Sensor Test
1) Check and repair vacuum hose connections at throttle body
and MAP sensor. Check output voltage at MAP sensor connector terminal
"B" (marked on sensor body) with ignition on, engine off. Voltage
reading should be 4-5 volts. If engine is hot and idling in Neutral,
reading should be 1.5-2.1 volts. Check voltage at terminal No. 33 of
ECU connector. Reading should be same as that at terminal "B" on MAP
sensor connector. See Fig. 4.
2) With ignition on, check MAP sensor supply voltage at
terminal "C". Reading should be 4.5-5.5 volts. Same voltage reading
should be obtained at terminal No. 16 on ECU harness connector. If
necessary, repair or replace wiring harness. Using Diagnostic Tester
(MS 1700), test ECU if necessary. Check MAP sensor ground circuit at
terminal "A" and terminal No. 17 of ECU connector. Repair wiring if
necessary.

NOTE: When diagnosing fuel system problems using following
procedures, no specialized service equipment is needed.
Following diagnostic procedures are NOT applicable if
special tester M.S. 1700 is used.
Six different test flow charts are used to fully evaluate
fuel injection system:
TEST 1: IGNITION OFF
This test checks that system power provides for ECU memory
keep-alive voltage.
TEST 2: IGNITION ON: POWER
This test checks system power function and fuel pump power
function.
TEST 3 & 3A: IGNITION ON: INPUT
These tests check the following components and their
circuits: closed throttle (idle) switch, Throttle Position Sensor
(TPS), MAP sensor, A/T gear selector switch, Coolant Temperature
Sensor (CTS) and MAT sensor. Coolant temperature and MAT sensors are
tested in cold condition. This procedure also checks all interrelated
wiring circuits as well.
TEST 4 & TEST 4A: SYSTEM OPERATIONAL
These tests check engine start-up circuit, fuel injector,
"Closed Loop" air/fuel mixture function, coolant temperature sensor
function, MAT sensor function, detonation sensor "Closed Loop"
ignition retard/advance function, EGR valve and canister purge
solenoid function, idle speed control and A/C control functions.
TEST 5: BASIC ENGINE
This test indicates failures in related engine components
that are not part of fuel injection system.
TEST 6: MANUAL TRANSMISSION UPSHIFT
This test checks upshift indicator light function on vehicles
with manual transmissions.
Fig. 5: Jeep/Renix Fuel Injection ECU Connector
Courtesy of Chrysler Motors.
REMOVAL & INSTALLATION

COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Allow engine to cool down. Disconnect CTS wiring harness.
Remove CTS from intake manifold and rapidly plug hole to prevent
coolant loss. Install replacement CTS and connect CTS wiring harness.
FUEL INJECTOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.
Removal
Remove air cleaner assemby. Remove injector wiring
connector. Remove injector retainer screws and clip. Using small
pliers, carefully grasp center collar of injector between electrical
terminals and carefully remove injector with lifting/twisting motion.
Discard both "O" rings. See Fig. 6.
Installation
1) Using light oil, lubricate new upper and lower "O" rings.
Install "O" rings in housing bore. Install back-up ring over upper
"O" ring. Position replacement injector in fuel body.
2) Center nozzle in lower housing bore and use a
pushing/twisting motion to seat injector. Align wire connectors in
proper orientation. Install retainer clip and screws. Connect
injector wiring. Install air cleaner.
Fig. 6: Fuel Injector & Throttle Body Assembly
Courtesy of Chrysler Motors.
FUEL PRESSURE REGULATOR

Removal & Installation
Remove throttle body assembly as previously described.
Remove Torx head retaining screws. Remove throttle position sensor
from throttle shaft lever. To install, reverse removal procedure.
Adjust TPS after installation. See ADJUSTMENTS in this article.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
Removal & Installation
Disconnect wire harness connector from MAT sensor. Remove
MAT sensor from intake manifold. To install, reverse removal
procedure. See Fig. 7.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal & Installation
Disconnect wire harness connector, vacuum hose, and
retaining nuts from MAP sensor. Remove sensor from firewall. To
install, reverse removal procedure.
ELECTRONIC CONTROL UNIT (ECU)
Removal & Installation
1) On Wrangler, remove passenger assist handle and glove box
assembly. Remove ECU bracket retaining nuts from engine compartment
side of firewall. Disconnect ECU wiring harness. Remove ECU from
bracket. To install, reverse removal procedure.
2) On all other models, remove retaining screws and bracket
that supports ECU above accelerator pedal. Remove ECU and disconnect
wiring harness. To install, reverse removal procedure.
EGR VALVE
Removal & Installation
Disconnect vacuum hose from EGR valve. Remove bolts which
hold EGR valve to intake manifold. Remove valve and discard gasket.
To install valve, reverse removal procedure. Always use new gasket.
See Fig. 7 .
TROUBLESHOOTING AND DIAGNOSIS

Fig. 23: TEST 5: BASIC ENGINE

2.5L TBI
1) Adjustment of fuel pressure is required after replacement
of pressure regulator. Remove air inlet from throttle body. Connect
tachometer to diagnostic connector terminals D1-1 and D1-3. Connect
fuel pressure gauge to fuel body pressure test fitting.
NOTE: Some TBI models do not have a pressure test fitting on
throttle body. Use Fitting (PN 8983 501 572) for this
purpose.
2) Start engine and accelerate to 2000 RPM. Turn adjustment
screw to obtain 14.5 psi (1.02 kg/cm
) fuel pressure. Location of
adjustment screw is on bottom of regulator. Install lead seal ball to
cover regulator adjustment screw after adjusting fuel pressure to
specification. Turn ignition off. Disconnect fuel pressure gauge.
Install cap on test fitting. Install air inlet.
NOTE: To increase fuel pressure, turn adjustment screw inward. To
decrease fuel pressure, turn adjustment screw outward.
4.0L MPFI
1) Remove cap from pressure test port in fuel rail. Connect
Fuel Pressure Gauge (J-37730-1) to pressure fitting. Start vehicle.
Pressure should be approximately 31 psi (2.7 kg/cm
) with vacuum
hose connected to pressure regulator.
2) Pressure should be 39 psi (2.74 kg/cm
) with vacuum
hose removed from regulator. If fuel pressure is not to
specifications, check for kinks or restricting bends in fuel supply
and return lines. Check fuel pump flow rate. Pump should deliver
minimum of 1.06 quarts (one liter) of fuel per minute with fuel
return line pinched off.
3) If flow is inadequate, check system for plugged fuel
filter or filter sock. Fuel pump flow rate can be checked by
connecting a hose to fuel test port on fuel rail and inserting other
end in clean container.
4) To operate fuel pump, install a jumper wire into
diagnostic connector terminals D1-5 and D1-6. Pinch off fuel return
line to ensure that no fuel returns to fuel tank. If fuel pressure is
still not to specifications and fuel flow is normal, replace
regulator.
REMOVAL & INSTALLATION
FUEL PUMP
Removal (2.5L TBI)
1) Disconnect battery cables. Ensure fuel level is less than
1/2 for this procedure. Remove fuel outlet and return hoses. Remove
sending unit wires. Remove sending unit retaining lock ring.
2) Remove sending unit/pump assembly with "O" ring seal.
Disconnect fuel hose from fuel pump. Disconnect wires from fuel pump.
Remove fuel pump from sending unit.
Installation
Clean seal contact are of fuel tank. Install new "O" ring
seal. Install a new filter on end of suction tube. Position sending
unit/pump assembly in tank. To complete installation, reverse removal
procedure. Start engine and check for leaks.
CAUTION: Fuel leaks can develop from over tightening sending
unit/pump during installation.